Metallic thermometer



(NbModeL) I a. B. ST.-JOHN METALLIC THERMOME TER. 7

No. 355,281; Patented Dec. 28, 188

UNITED STATES PATENT OFFI E.

GEORGE B. ST. JOHN, OF BOSTON, MASSACHUSETTS.

METALLIC THERMOMETER.

I SPECIFICATION forming part of Letters Patent No. 355,281, datedDecember 28, 1886.

(No model.)

' To all whom it may concerrt:

Be it known that I, GEORGE B. ST. JOHN, of Boston, county of Suffolk,State of Massachusetts, have invented an Improvement in Thermometers, ofwhich the following description, in connection with the accompanyingdrawings, is a specification, like letters on the drawings representinglike parts.

My invention relates to'a thermometer of that class in which a hand orpointer is rotated by the movement caused by the unequal expansion ofthe different parts of a helix composed of metals having different ratesof expansionby heat.

The invention has for its object to enable the parts to be readilyadjusted to give the correct indications of temperature; and it consistsin the combination and arrangement of parts, substantially ashereinafter particularly set forthand claimed. I

In the accompanying drawings, illustrating the invention, Figure l is afront elevation; Fig. 2, a side elevation on a larger scale, the dialbeing broken off at each end. Fig. 3 is a top plan View of parts at theleft-hand end of Fig. 2; and Fig. atis a rear elevation of the' parts atthe right-hand end-of Fig. 2.

The operative parts are supported in a frameplate, a, connected with thedial I), graduated to co-operate with a hand or pointer, 0, fastenedupon an arbor, cl, which passes through the plate a, and has a pivotalbearing on an arm or bracket, 6, connected with the said plate- The saidarbor d is provided with a pinion, f, meshing with a segmental gear, 9,the arbor g of which has pivotal bearings in the bracket 6 and anotherbracket, 0, mounted on the frame a. The segmental gear 9 is providedwith an arm or projection, h, which has securely attached to it one endof the spiral ribbon or expansion-helix t, composed of outer and innerlayers of metals, alloys, or their known equivalents, having differentratesof expansion by heat, so that the expansion or contraction of thesaid materials produced by a change in their temperature will produce arotary movement of one end of the coil relative to the other in theWell-known manner. In order that such rotary movement may produce amovement of the pointer c, it is necessary that the opposite end of thehelix 2' to the one connected with the arm hand gear 9 should be rigidlyheld with relation to the frame-work a.

In order to enable the position of the helix ito be varied and adjustedquickly, as well as 5 5 the length of the effective portion between thetwo points of attachment of its ends, it is adjustably connected with anattachingarm, it, having a stud, k, fitted to move freely in a socket ofa post, m, fixed upon the plate a, the 5 saidstud and attaching-armbeing rigidly held in any desired position in the post at by means of asetscrew, 0, or equivalent, preferably operated from the face of thedial.

In putting together the thermometer, which 5 is intended to bemanufactured in quantities, the end of the helixt is passed through aslot in the arm is, and made fast by a locking device or set-screw, p.The thermometer is then permitted to come to a definite known tem- 73perature-as, for example, by immersing it in melting snow or iceand thehand a is then. turned to the proper graduation of the dial forinstance, 32, if the graduation is in accordance with the Fahrenheitscale. The setscrew 0 is left loose while this operation is takingplace, so as to permit the arm to turn freely, keeping the helix 4.perfectly free or without strain while the pointer is being thus set,after which the set-screw 0 is tightened, thus locking the arm is andfixing the point of attachment of the stationary end of the helix Thethermometer will next be subjected to another known temperature, and therotary movement of the end of the helix attached to the arm h, withrelation to the stationaryend fastened to the arm It, will cause thepointer to turn. If the pointer arrives at the proper graduation for theknown temperature, it will be understood that the thermometer is inadjustment; but if the said pointer does not move exactly the properdistance, it will be understood that the helix is too long or too short,and the proper adjustment will be made by loosening the set-screw p andtaking up or lengthening the said helix, as may be required. This changein length of the helix will necessitate the readjustment of itsposition, which may be readily effected by loosening the setscrew 0 andturning the pointer to the proper place, after which the set-screw 0 isagain tightened and the thermometer tested by another change intemperature'to see if the helix has been made of the proper length.

ICO

It is immaterial at which end of the helix the adjustment of its lengthis made, and by the said adjustment it is possible to make the dials ofa series' of instruments all uniform, and the helices and other parts asnearly uniform as possible, the said adjustment in length of the helixbeing sufficient to compensate for the unavoidable inequality in thesaid helices, which has heretofore necessitated an especial graduationfor the dial of each individual thermometer.

By having the entire helix movable before its end is finally locked ormade stationary with relation to the plate, the inconvenience ofdisengaging the gearingf and g, or of moving the pointer on its arbor,is avoided, and the thermometers, the parts of which are made inquantities, can be readily and quickly assembled and adjusted with greataccuracy.

By arranging the helix longitudinally parallel with the dial, there isan economy of space, and the parts are made very accessible.

I claim- 1. The graduated scale, the pointertherefor, a pinion on thearbor of such pointer, and a segmental gear meshing with said pinion,

and provided with an arm supported on a rock-shaft, combined with anexpansion-helix attached to said arm at one end, and supported inadjustable bearings at its other end to vary 3o itsefi'ective lengthand, axial position, substantially as described.

2. The expansion-helix, and pointer actuated thereby, combined with thedial and the attaching-arm for the said helix, provided 5 with a studhaving a pivotal movement, and a set-screw therefor operated from theface of the dial, substantially as described.

3. The combination, with the graduated dial and its pointer, of thehelix longitudio nally parallel with the dial, the adjustable hearing atone end, and the gearing connect ing the helix and pointer at the other,substant-ially as shown and described.

' In testimony whereof I have signed my 5 name to this specification inthe presence of two subscribing witnesses.

GEORGE E. ST. JOHN.

Witnesses:

J os. P. LIVERMORE, W. H. Sresrron.

